1. Field of the Invention
The present invention relates to an ink jet apparatus capable of practicing an improved recovery operation to be performed when ink tank cartridges are replaced.
2. Related Background Art
As an ink jet recording apparatus, there has hitherto been known a method whereby to perform recording by ejecting ink from the recording head utilizing the pressure which is exerted by changes in the state of ink using electrothermal transducers. In a recording apparatus of this kind, the dissolved gaseous component is deposited in ink due to boiling of the ink. As a result, there may be some cases where bubbles are not resolved again and are caused to remain in the recording head. If this condition is repeated, the remaining bubbles gradually enter the ink passage by the flow of ink, and may hinder the ejection of the ink. Also, there is a case where the remaining dissolved gas in ink is deposited due to the environmental changes and unintentionally developed; thus hindering proper ink ejection.
According to experiments conducted by the inventor hereof, the bubbles thus developed may become a size presenting such a problem when 30 to 40 A-3 sized sheets are printed with 100% duty. Therefore, in order to avoid producing any adverse effects on the ink ejection, such bubbles must be removed. For a conventional ink jet recording apparatus, there is known a method as general means for removing bubbles in which ink and bubbles in the recording head are sucked by providing an airtight cap airtightly covering the front end of the recording head to generate negative pressure in the cap in such a state by means of a pump connected to the cap.
However, in the above-mentioned conventional example, if there is a staged portion between a common liquid chamber and an ink passage as shown in FIG. 5A, such portion is stagnated to make it easier to collect the bubbles. In addition, not much ink flows even when ink is sucked and thus it becomes difficult to remove bubbles, particularly small ones. Also, when a target bubble is large as shown in FIG. 5B, the bubble is partially exhausted with the majority thereof still remaining as shown in FIG. 5C, which will be again developed while several sheets are being printed; hence creating a problem that the ingression of bubbles to the nozzles may take place. As described earlier, the liquid passage of the recording head is divided into a plurality of nozzles 14 for ejecting recording liquid each having an electrothermal transducer 18 and a common liquid chamber 15, serving as a reservoir, for; ink to be supplied to the nozzles 14 through filters 20 between a substrate 19 and a ceiling plate 17. Now, since the common liquid chamber needs a capacity which is as large as several tens to several hundreds of times that of the nozzle portion, it is inevitable that rapid configurational changes occur between the nozzle portion and the common liquid chamber to generate stagnation at that point. As a method to solve a problem of this kind, there is disclosed, for example, a method in Japanese Patent Laid-Open Application No. 63-224958 wherein airtight cap made of a resilient material is provided to cover the recording head and still in such a state, the cap is depressed so as to deform the resilient material. Thus, the air in the cap is compressed into the interior of the head through the discharging ports thereof to allow it to be combined with the air which has pressed the bubbles in the ink passage and the common liquid chamber and then in a state that the liquid passage is made empty, ink is again filled in the interior of the recording head by the suction of a pump. This method, however, may present a possibility that the unwanted liquid forms dust and the like in the cap which is also compressed into the nozzles simultaneously because this method requires the air to be compressed from the front end of the foregoing head. Also, the resilient material of the cap must be deformed for this purpose. Therefore, it is necessary that the resilient material to be used is more durable, and that a special mechanism is arranged to deform it; thus creating a problem that the structure becomes inevitably complicated.
Also, as another means in this respect, there is a method such as disclosed in Japanese Patent Laid-Open Application No. 62-109655 wherein a branch is provided for a part of the ink supply passage for the recording head and the ink tank cartridge and by enabling it to be opened to or closed from the atmospheric air by the use of a valve or the like in order to empty from such a branched portion to the recording head portion with the air inducted therefrom; thus obtaining the same effect as the foregoing method whereby to compress the air from the cap. Although this method has an advantage that the induction of air can be conducted appropriately, it still presents a problem that its mechanism becomes extremely complicated in order to provide a portion which can be opened to the atmospheric air for the ink supply passage.
Now, the bubbles are generated not only in the recording head portion, but also in the ink supply passage from the ink tank cartridge to the recording head depending on the environmental changes. The bubbles of these types cannot be removed sufficiently by any one of the foregoing methods and as ink supply is repeated, the bubbles in the ink supply passage may enter the head portion.